Growing Media, Raft Beds, pH & Beneficial Bacteria
|CLAY BALLS||3/4 INCH GRAVEL||PEA GRAVEL|
Clay Balls are commonly used in Hydroponics and Aquaponics and are organic, lightweight and pH neutral. This is a big adventage over other grow media, because you are easily able to move plants without disturbing delicate root systems. Clay balls are available at Hydroponic stores or online. Wash clay balls well before using.
Three-quarter inch gravel is heavier but preferred by some Aquaponic gardeners because it is not likely to form dead spots, otherwise known as anerobic spots. Do not use gravel containing limestone since it causes the pH to be too high.
Pea Gravel is also used in Aquaponics beds. It is relatively inexpensive and available at your local Home and Gardening Stores.
Maintaining pH Levels
Purchase a Test Kit that measures pH, Ammonia, Nitrites and Nitrates.
Starting a new system requires that you test your water to determine the pH level. Fish perfer a pH of 7 and plants prefer a pH of 6-6.2, so a good pH that will satify both plants and fish is 6.2-6.4. When the pH is above 7 plants get what is called "nutrient lockout" where iron and magnesium are not absorbed.
Starting a new system also requires what is called "cycling". Cycling occurs as nitrosomanas and nitrobacter bacteria benebicial bacteria begin to grow in the growbeds. This can be accomplished by adding a small amount of pure ammonia, fish food or even live fish to the tank. Be cautious with live fish and do pH and ammonia testing before adding fish so that you don't kill your starter fish. The system needs to "cycle" about 60 days and you should notice that your pH becomes more acid (closer to 6) as it matures. When this happens you will need to add 3 tablespoons of lime per 250 gallon total water volume. Do not use dolomite as it contains other chemicals. (Growbeds are about half water so add the gallons size of your fish tank to half the gallons size(s) of your growbeds to determine the amount of lime needed).
Example: 300 gallon fish tank plus two 120 gallon growbeds. 300+60+60=420 total water volume, so you would use 5-6 tablespoons of lime.
Retest the pH after 24 hours and add a small amount more lime if necessary.
Once the Nitrate level is optimum you can add more fish and plants to the growbed. New fingerlings may require a salt bath in order to clean them of parasites and fungus. Aquarium or swimming pool salt can be used. Fingerlings should be placed in pH adjusted water and completely dissolved salt at the ratio of 4-6 tablespoons per gallon of water for 10-20 minutes. Watch your fingerlings and if they start to roll-over then they are too stressed and put them back in fresh water immediately. What this does is shock the parasites and fungus and restores their mucous membrane. Maintenance testing of your water should be done once a week and sample taken as it goes into the grow bed. Test for pH, ammonia, and nitrates.
Redworms and the Aquatic Eco System
The addition of redworms is essential to keeping root blockages from forming. If your system has been running for a while and pH levels have been established but your pH tests are high then you may have a root blockage. Check the growbed for plants with large root systems that may have become blocked or anerobic. Pull the grow media away from the roots. The addition of redworms is essential to keeping root blockages from forming. These redworms can be obtained at garden supply stores and online.
Our raft beds are made from 1.5" polystyrene. We use 2" net pots for growing lettuces, spinich, and herbs right on top of out fish tank, which also serves as a cover for the tank and adds insulation. The foamboard has holes that can be cut with a hole saw that is the correct size for the net pots you use. Most net pots have a lip so that the plant will not fall through the foamboard. If you are using a 2” net pot then a 1 7/8 inch hole saw would probably work for you, but try it out on a scrap of foamboard before cutting all the holes. The foamboard floats on top of the growbed or in some cases the aquaculture tank (see diagram under component parts) and roots are fed directly by the nutrient-dense water.
Delicate root systems are beginning to form as net pots containing seedlings are placed in the nutrient-dense fish water. Once the system has cycled, the beneficial bacteria grow on the back on the foamboard thus converting the ammonia from fish waste into nitrates which feed the plants.
Mature roots grow quite long in the nutrient-dense water. Much of the beneficial bacteria needed for feeding the plants is harbored on the back of the foamboard and on the roots. When the system is fully cycled you will notice a slimy coating on the underside of the foamboard.